Thread roll dies

ABSTRACT

A thread rolling die for forming dissimilar thread forms on a cylindrical bolt blank. The die forms a continuous constant pitch spiral thread on the cylindrical blank with a truncated thread form at one end and a full thread form on the remainder thereof. Additionally, the die is constructed to include depressions in its face which form cam-shaped lobes on the truncated portion of the screw thread to provide a unitary thread rolling screw.

United States Patent Carpenter et a]. [4 Aug. 22, 1972 [54] THREAD ROLL DIES 3,517,717 6/1970 Orlomoski ..72 /88 Inventors: Carpenter, Breed Ave-1 p i 19075; Albert FOREIGN PATENTS OR APPLICATIONS Rlchboro 18956 210 236 7/1960 A t 85/46 us r1a [221 filed! 4, 1970 701,864 1/1965 Canada ..10/152 T 2 App}. 9 9 943,575 12/1963 Great Britain ..85/46 Primary Examiner-Charles W. Lanham [52] US. Cl. ..72/88, 10/10, 72/469 Assistant Combs [5 Int. ..B2lh Attorney-Andrew L Ney [58] Field of Search.....10/10, 152 T; 72/88, 90, 469,

72/470; 85/46, 47, 48 [57] ABSTRACT R f A thread rolling die for forming dissimilar thread [56] e erences cued forms on a cylindrical bolt blank. The die forms a con- UNITED STATES PATENTS tinuous constant pitch spiral thread on the cylindrical blank with a truncated thread form at one end and a sgnfiinds thread on the remainder thereof. 4985232 5/1 93 S e on l 9 tionally, the die is constructed to include depressions McManus in c f h p lobes on the trun 2,183,689 12/1939 018011 Gated portion of the Screw thread to provide a unitary 2,352,540 6/1944 Hanneman ..72/88 thread rolling Screw 3,426,642 2/1969 Phipard ..85/46 3,426,820 2/1969 Phipard ..85/46 6 Claims, 4 Drawing Figures THREAD ROLL DIES This invention relates to thread rolling dies and in particular to a die for rolling thread forming screws.

The thread forming screws to be formed by the rolling dies of this invention are similar to those disclosed in copending U.S. Pat. application, Ser. No. 802,774, filed Feb. 27, 1969, now U.S. Pat. No. 3,527,136 which disclosure is incorporated herein by reference. In brief, that application describes a thread forming screw which includes a shank portion having a pilot end adapted to be received in an unthreaded hole in a metallic member. The screw includes a continuous constant pitch thread having a truncated form on its pilot end and a full form on the remainder of the shank. Protruding from the truncated thread form are a plurality of cam-shaped thread forming members which initially align the screw within the unthreaded hole and,

as the screw is rotated, roll form an internal thread configuration in the hole. In this manner, the hole in the metallic member is threaded and then engages and retains the full form threads of the screw as it is rotated within the hole.

Thread rolling dies are a known means for rolling a thread form on bolts, studs, etc., and are generally rectangular plate members having one surface thereon serrated. These serrations include alternate ridges and grooves, which conform in plan to the shape of the screw threads to be rolled. The serrations run the length of the die face and are inclined with respect to the longitudinal axis of the die face at an angle corresponding to the lead angle of the threads to be rolled. The dies are used in mating pairs with their serrated faces facing each other. A cylindrical blank of the bolt to be threaded is placed between the dies at one end thereof. The dies are then pressed against theshank and one of the dies is moved longitudinally, thereby rotating the blank about its axis and roll forming the screw threads thereon.

Dies of the type described have been used in the past to roll single thread forms on cylindrical blanks and have been found to be a relatively fast and efiicient method of forming threaded members. However, when rolling dissimilar thread forms on a blank, it has not been uncommon, in the past, to roll each thread form separately in two or more thread rolling operations. Thus, the cost of bolts with dissimilar thread forms is quite expensive.

Accordingly, it is an object of the present invention to provide thread rolling dies which can roll a constant pitch, dissimilar thread form on a bolt blank in a single operation. It is another object of this invention to provide thread rolling dies which can roll a constant pitch dissimilar thread form on a blank so that a smooth transition thread connects each of the different thread forms. It is a further object of the present invention to provide thread rolling dies to accurately align and form different thread forms on a bolt blank wherein one of the thread forms includes thread rolling lobes. A still further object of the invention is to provide thread rolling dies that are simple and durable in construction, economical to manufacture, and highly efiicient in' operation.

In accordance with one embodiment of the present invention a generally rectangular die plate is provided and includes two generally rectangular longitudinally extending areas on one face thereof which mate with each other along a transition line extending generally parallel to the longitudinal axis of the die plate. Each area contains a group of serrations which are inclined with respect to the longitudinal axis of the die at an angle corresponding to the lead angle of the thread to be rolled on a cylindrical blank and each group of serrations includes alternate ridges and grooves which run the length of their respective areas and which mate with each other along the transition line. The crests of all the ridges lie in a common horizontal plane and serve to form the roots of the thread to be rolled. The depth of the grooves between the ridges in one of the two rectangular areas is greater than the depth of the grooves between the ridges in the other rectangular area so that the deeper grooved area defines the complement of a full thread form and the shallower grooved area defines the complement of a truncated thread form. Arcuate cavities of various depths are formed in the shallower grooves of the die to define the complement of cam-shaped thread forming members which are to be rolled on the truncated thread form. In use, two complementary dies are provided to roll the thread forms on the cylindrical blanks.

Further objects and advantages of the present invention will become apparent from the following description when considered in conjunction with the accompanying drawings wherein:

FIG. 1 is a diagrammatic plan view of a preferred embodiment of one of the mating dies prepared according to the present invention;

FIG. 2 is a sectional view taken on line 2-2 of FIG.

FIG. 3 is a sectional view taken on line 3-3 of FIG. 1; and

FIG. 4 is an elevational view of a roll form thread rolling screw prepared by the die of the present invention.

To facilitate an understanding of the present invention, a brief description of a bolt rolled by a preferred embodiment of the invention will be provided with reference to FIG. 4 of the drawing.

The bolt 30 includes a shank portion 31 having a pilot end 35 and is similar to the bolts disclosed in the above noted copending application, Ser. No. 802,774 now U.S. Pat. No. 3,527,136. Shank 31 includes a continuous thread 33 having a truncated form 36 on pilot end 35 and a full form 34 on the remainder of the shank. Extending radially outwardly form the truncated thread form 36 on pilot end 35 and spaced from the end 38 of shank 31 are cam-shaped protrusions or lobes 40, 40', 42 and'44 which are adapted to engage the wall of an unthreaded bore or hole in a workpiece (not shown) to roll form an internal thread surface therein.

Truncated threads 36 have a smaller diameter than the hole in which the thread rolling screw fastener 30 is to be placed and the first few threads are smooth to facilitate initial insertion of the screw 30 in the hole. Once the fastener member 30 has been placed in an unthreaded bore, it is rotated therein causing the first cam-shaped lobes 40 and 40 to engage the unthreaded wall surface of the hole.

Lobes 40, 40', 42 and 44 are generally eliptically shaped members in plan and incline outwardly form a thickened base portion to converge and form a linearly disposed thread rolling surface 45. As seen in FIG. 4, lobe 44 extends outwardly further than lobe 42 which, in turn, extends outwardly further than lobes 40 and 40'. The latter protrusions are substantially equal in height.

As fully explained in copending application, Ser. No. 802,774, initial protrusions 40, 40' serve to score and partially form mating threads in the inner surface of the hole and to axially align the screw therein so that it is co-axial with the hole in which it is placed. As the screw is progressively engaged with the bore, the progressively larger protrusions 42 and 44 successively engage theintemal surface of the hole, and follow and enlarge the scored indentation formed by protrusions 40 and 40. The protrusions 42 and 44 are oriented along the lead line of the threads to be formed and spaced from protrusions 40, 40, a distance equal to the pitch of the threads. Thus, proper scoring along the same spiral followed by protrusions 40, 40 is assured. The progressively increasing size of protrusions 40, 40', and 42 and 44 permit a gradual scoring and engagement with the inner surface of the bore to facilitate plastic deformation of that surface. In this manner, screw 30 forms mating internal threads in a workpiece for engagement by its full form threads 34.

With reference now to FIGS. 1 and 3 of the drawing, there is shown one of a mating pair of thread rolling dies formed from a substantially rectangular block of steel, which may be hardened tool steel or the like. Die 10 has one face 11 thereon serrated as at in two sections 12 and 14 which are separated by a transition line 16 extending parallel to the longitudinal axis of the die. Serrations 20 extend across both sections 12 and 14 to form parallel ridges 18 have relatively flat crests 22, each of which lie in a common horizontal plane as seen in FIG. 3. FIG. I diagrammatically illustrates the complete thread rolling die, wherein the solid lines represent the base width of ridges 18 in sections 12 and 14.

Adjacent ridges l8 define grooves 26 and 28 in sections 12 and 14, respectively. Grooves 26 and 28 have generally flat bottom fades and, as best seen in FIG. 3, grooves 28 are deeper, as measured from the plane of crests 22, than grooves 26. As will be more fully described hereinafter grooves 26 and 28 are complementary to and form truncated thread form 36 and full thread form 34, respectively, on the bolt 30 illustrated in FIG. 4. It should be understood, of course,.that the relationship of the grooves and ridges just described results from the configuration of the two thread forms to be rolled on bolt 30 and that if other thread forms are to be rolled, the relationship of the grooves and ridges will vary accordingly.

Serrations 20 are inclined with respect to the longitudinal axis of block 10 at an angle which corresponds to the lead angle of the threads to be rolled. The spacing 5 (see FIG. 3) between each successive ridge and each successive groove is equal to the pitch of the threads to be rolled, and this spacing is the same in both sections 12 and 14 so that both the truncated and full form of the single, continuous thread on bolt 30 have the same pitch.

Since serrations 20 extend across both sections 12 and 14, the serrations in one section must be aligned with the serrations in the other section. Thus, ridges 18 extend continuously across transition. line 16 and grooves 26 and 28 form a continuous groove across the transition line so as to form a smooth transition portion 39 between full thread form 34 and truncated thread form 36 on bolt 30.

As previously noted, truncated thread form 36 on pilot end 35 is formed by shortened grooves 26 in section 12 of die 10. To form the various lobes 40, 40, 42 and 44 on thread form 36, certain grooves 26 areprovided with corresponding groups of cavities 50, 50, 52 and 54, each containing a series of cavities. Groups 50 and 52 each contain three cavities, a, b and c, and groups 50 and 54 each contain two cavities, a and b. Each cavity in a group has the same depth which corresponds generally to the height of the lobe which it will form. For example, cavities 52a, b and e have a depth d, note FIG. 3, which substantially corresponds to the height of lobe 42 above the smooth outer surface of truncated thread form 36. Similarly, cavities 500, b and e have a depth d, again note FIG. 3, which substantially corresponds to the height of lobe 40 above the smooth outer surface of truncated thread fonn 36. Thus, there are four groups of cavities which correspond to the four lobes shown in the embodiment of the bolt seen in FIG. 4.

As seen in FIG. 1, each of the cavities in a group, e.g., group 54, are of like size and have their centers aligned and substantially equally spaced along a line parallel to the longitudinal axis of the die. The longitudinal spacing between the centers of the cavities in a group is substantially equal to the circumference of the bolt to be rolled so that during the rolling operation a lobe formed in the first cavity of a group, 54a, for example, will mate with a similar complimentary cavity 54b as the lobe is again rolled into contact with the die on the next revolution and again with cavity 540 on the final revolution. The .use of a series of cavities to form a single protrusion serves to accommodate and finish formthe protrusions which are initially formed in the first cavity of a particular group. It is noted that the spacing between cavities in a group is not exactly equal to the circumference of the bolt being rolled since the roll pressure applied to the blank and the amount of pure roll or slippage of the blank with respect to the die will effect the rotation thereof. Thus, the exact spacing must be separately determined for each size screw.

In practice, to roll a thread on a cylindrical blank member, a pair of complementary dies are placed substantially parallel to each other in overlapped relationship so that one die is leading and the other is trailing. A cylindrical blank is placed between the dies which are then pressed toward each other to compressively contact the cylindrical blank. The leading die is held stationary and the trailing die is moved longitudinally, thereby rolling the cylindrical blank about its longitudinal axis. The movement of the dies in conjunction with the compressive force placed thereon,- causes the material of the cylindrical blank to flow into the groove portions and cavities of the dies and out of" the ridge portions thereof to thus form the dissimilar thread configurations and cam-shaped protuberances on the blank. The flow of material on the bolt blank is actually threefold with the main portion of the material flow being along the helix angle formed by the inclined serrations. Another portion of the material flows into the grooves of the die and there is also a portion of the material which flows upwardly toward the top of the die. The head or tool engaging end 58 of bolt 30 is formed in a separate operation before the thread forming process.

To assure that the lobes on the bolt are formed to their full height, it has been found that the upward and helical flows of material on the blank may be advantageously utilized by providing a fiat zone 60 in section 12 of the die in the area immediately adjacent the first cavities contacted by the bolt, i.e., cavities 40a and 50a. Accordingly, no thread forming will occur on the blank in the vicinity of the desired lobes until the blank engages the first cavities. Prior to the engagement of the blank with the first cavities, the material on the blank flowing helically and upwardly will accumulate on the face of the blank in the area where the lobes are to be formed. The accumulated material along with the usual blank material will then be forced into the first cavities and fully form the cam-shaped lobes 40, 40', 42 and 44.

Zone 60 is located substantially on the same plane as grooves 26. As seen in FIGS. 1 and 2, certain of the ridges 18 in the first section 12 of die are tapered downwardly towards the plane of the grooves 26 to form a smooth transition ramp 62 leading into and out of zone 60. It has been found that the height of the cam-shaped lobes formed on the blank will be approximately 85 percent of the cavity-depth when a ramp of this character is included in the dies.

While only one of the pair of dies used in the thread forming operation is illustrated in the drawings, it should be evident that the mating die is similar in design and complimentary to the die illustrated. In addition, both dies are bead-blasted to minimize slippage of the cylindrical blank as it progresses through the thread rolling operation.

It is thus seen that the present invention provides thread rolling dies which forms a constant pitch thread with dissimilar thread forms and, more particularly, which forms self-retaining thread rolling screws of the character described.

It is to be understood also that the foregoing disclosure of the preferred embodiment of this invention is illustrative and exemplary only, and that the invention is not limited to the specific embodiment shown and described, since many modifications and changes may be made therein without departing from the inventive concept.

What is claimed is:

l. A thread rolling die configuration for rolling dissimilar thread forms having a like pitch, on a cylindrical blank, comprising a substantially rectangular die member, one face of said rectangular member having first and second thread form sections, said first and second sections having serrations thereon comprising a plurality of substantially longitudinally extending ridges having crests lying in a common plane, the longitudinal axis of said ridges being inclined relative to the longitudinal axis of said die member at an angle corresponding to the lead angle of the threads to be rolled, said serrations defining grooves between said ridges, wherein the grooves in said first sections have a greater depth from said lane th the grooves in said secogd sections and cert n of sai grooves in sat secon sectron ave generally arcuate longitudinally extending depressions therein, said second section including a generally flat zone in the plane of said grooves in said second section interrupting a plurality of said serrations intermediate their ends, said plurality of serrations including longitudinally inclined ridge sections adjacent said zone to define a die ramp portion leading into and out of said zone, wherein when a cylindrical blank is rolled between a pair of mating dies to form a thread form thereon material of the cylindrical blank is caused to How within the mating dies to accumulate in the area corresponding to the flat zones to provide for additional material of the cylindrical blank to be formed within the arcuate longitudinally extending depressions in said second sections.

2. The thread rolling die as defined in claim 1 wherein certain of said ridges in said second section are longitudinally tapered in an intermediate section thereof towards their respective grooves to define a die ramp section.

3. The thread rolling die as defined in claim 1 wherein certain of said serrations extend through both said first and second sections and define dissimilar grooves in each respective section.

4. The thread rolling die as defined in claim 1 wherein certain of said arcuate depressions have a greater depth from said plane than the remaining depressions.

5. The thread rolling die as defined in claim 4 wherein said depressions are generally cam-shaped.

6. The thread rolling die as defined in claim 3 wherein said first and second sections are separated by a longitudinally extending transition line and wherein said certain of said serrations extending through both said first and second sections are joined to each other along said transition line. 

1. A thread rolling die configuration for rolling dissimilar thread forms having a like pitch, on a cylindrical blank, comprising a substantially rectangular die member, one face of said rectangular member having first and second thread form sections, said first and second sections having serrations thereon comprising a plurality of substantially longitudinally extending ridges having crests lying in a common plane, the longitudinal axis of said ridges being inclined relative to the longitudinal axis of said die member at an angle corresponding to the lead angle of the threads to be rolled, said serrations defining grooves between said ridges, wherein the grooves in said first sections have a greater depth from said plane than the grooves in said second sections and certain of said grooves in said second section have generally arcuate longitudinally extending depressions therein, said second section including a generally flat zone in the plane of said grooves in said second section interrupting a plurality of said serrations intermediate their ends, said plurality of serrations including longitudinally inclined ridge sections adjacent said zone to define a die ramp portion leading into and out of said zone, wherein when a cylindrical blank is rolled between a pair of mating dies to form a thread form thereon material of the cylindrical blank is caused to flow within the mating dies to accumulate in the area corresponding to the flat zones to provide for additional material of the cylindrical blank to be formed within the arcuate longitudinally extending depressions in said second sections.
 2. The thread rolling die as defined in claim 1 wherein certain of said ridges in said second section are longitudinally tapered in an intermediate section thereof towards their respective grooves to define a die ramp section.
 3. The thread rolling die as defined in claim 1 wherein certain of said serrations extend through both said first and second sections and define dissimilar grooves in each respective section.
 4. The thread rolling die as defined in claim 1 wherein certain of said arcuate depressions have a greater depth from said plane than the remaining depressions.
 5. The thread rolling die as defined in claim 4 wherein said depressions are generally cam-shaped.
 6. The thread rolling die as defined in claim 3 wherein said first and second sections are separated by a longitudinally extending transition line and wherein said certain of said serrations extending through both said firsT and second sections are joined to each other along said transition line. 